Propargylic etherification

Important advances in propargylic etherification have come from the use of copper-based systems that achieve efficient, catalytic O-progargylation of phenols (Scheme 8).245,246 While the mechanism of this transformation remains unclear, the products of these reactions have been readily converted into chromenes through subsequent Claisen rearrangement,... 

An application of copper-catalyzed propargylic etherification has been reported in the synthesis of ustiloxin D (Equation (63)).248 Here, a quaternary center was generated from the unprecedented reaction of a phenol with an ethynyl aziridine. 

Scheme 7.15 Monoruthenium complex-catalyzed propargylic etherification of propargylic alcohols with various alcohols.

C-M bond addition, for C-C bond formation, 10, 403-491 iridium additions, 10, 456 nickel additions, 10, 463 niobium additions, 10, 427 osmium additions, 10, 445 palladium additions, 10, 468 rhodium additions, 10, 455 ruthenium additions, 10, 444 Sc and Y additions, 10, 405 tantalum additions, 10, 429 titanium additions, 10, 421 vanadium additions, 10, 426 zirconium additions, 10, 424 Carbon-oxygen bond formation via alkyne hydration, 10, 678 for aryl and alkenyl ethers, 10, 650 via cobalt-mediated propargylic etherification, 10, 665 Cu-mediated, with borons, 9, 219 cycloetherification, 10, 673 etherification, 10, 669, 10, 685 via hydro- and alkylative alkoxylation, 10, 683 via inter- andd intramolecular hydroalkoxylation, 10, 672 via metal vinylidenes, 10, 676 via SnI and S Z processes, 10, 684 via transition metal rc-arene complexes, 10, 685 via transition metal-mediated etherification, overview,... 

SN2-type Reactions Other leaving groups are also prone to undergo direct Sn reactions in the presence of Fe salts. Zhan and Liu described the direct Fe-catalyzed etherification of propargylic acetates by O-nucleophiles to give rise to a variety of functionalized propargylic ethers (Scheme 7.10) [14]. 

Synthesis.—Reisch, Mester, and co-workers have made important contributions this year by synthesizing the alkaloids furacridone (34) and ( )-rutacridone (37) for the first time. Regioselective etherification of 1,3-dihydroxy-jV-methylacridone (32 R = H) gave the acetal (33), which furnished furacridone (34) as the major product of acid-catalysed cyclization (Scheme 4). Claisen rearrangements of the 3-allyloxy-acridone (32 R = CH2CH=CH2) and the propargyl derivative (32 R = CH2C=CH) were also studied.18... 

Single-pot etherification of propargyl alcohols by alcohols (reaction 5) has been achieved by the rhenium(V)-oxo complex [ReOCl3(dppm)] bearing a diphosphine ligand, in NCMe, via a postulated allenolate intermediate R CH=C=C(R )-0-[Re]=0, which would undergo a nucleophilic addition of R OH at the R CH carbon. ... 

The substrate can be prepared by standard etherification reaction of a phenol derivative with a propargylic halide [lb]. Further carbon-carbon bond forming reactions of the terminal acetylenic carbon via metal acetylide provides a variety of substituted propargyl aryl ethers. Direct preparation using substituted propargyl ether is also possible. 

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